Porsche, and the Porsche crest are registered trademarks of Dr. Ing. h.c. F. Porsche AG.
This site is not affiliated with Porsche in any way.
Its only purpose is to provide an online forum for car enthusiasts.
All other trademarks are property of their respective owners.

History: After car-fire engine was out, heads taken off and some studs and springs replaced. Changed to quieter exhaust.Had trouble with dialing in the carburetors and changed the jets to the recommendations from EMPI (see above). It runs a lot better now.

Remaining complaint;The car runs pretty good (especially above 2,800) RPM.However; It takes me a while to leave after each stop (stop signs traffic lights etc) because the car want to stall. When I push the accelerator to quickly the RPM dips down, and car will die. Only when I ease on the paddle very gently, it will increase in RPM, and I can lift clutch at above 1,500 RPM.

I would certainly check the distributor, advance weights and dwell/timing first .I personally prefer 40 mm on that motor with the smaller ventures which makes off the line (your issue) more smooth with a faster air flow going into the motor.

You can do this two ways, both will cost the same.1) bring it to a shop with a Dyno to tune the carbs.2) throw smaller venturis in to increase the velocity of the charge...leave the rest as is. The increased velocity will draw in more fuel.

With smaller vents you will top out sooner, but you will increase lower rpm response.

I'm with Keith your mains are a a little fat. You need to get an lm2 wiifeband to remove the guessing. Aircooled.net I believe rents one. Also timing . Sounds like your getting too much gas or not enough timing, when you step on the pedal. What do the spark plugs look like?

Smaller venturis limit the overall amount of air, but only at peak rpm. You may sacrifice 2-300 Rpms by using smaller venturis but you will gain lower rpm performance.With carbs it's always a sacrifice somewhere.

You want a wide band air/fuel meter with a gauge.I use one with an 02 sensor stuffed up the tailpipe for tuning only.Others install them perminantly by welding a bung into the exhaust.Still more granular is to use EGT temps to monitor the mixture on each cylinder.

The nice part about carbs, at least our Weber's, is you can do these changes without opening up the carbs, so you could have a larger setup for racing, and a smaller setup for around town normal driving....swap takes minutes

The smaller vents will lose some power right @ the top but this will be in a range you rarely drive in,what you will see is a big improvement in bottom end power and response,any small loss in power will be soon forgotten once you have improved drivability .It was common knowledge earlier on with these carbs that they were not well setup ''out of the box'',this has been covered by aircooled.net and documented on theSamba.com.When tuning carbs always carry out a full ignition tune up first,good leads, plugs,cap,etc and correct timing,otherwise its a waste of time.

Hi Hans,everyone is going to have an idea about what your problem is, myself included(accelerator adjustment)but you really need to educate yourself and learn how to fix it yourself. Most mechanic nowadays are simply parts replacers, not diagnosing and problem solvers. Buy the book, read it and understand it, then adjust stuff.Make small adjustments, try it out between each adjustment. Its a great feeling when you figure it out yourself.I'm not sure about the hpmx book, but I have the dellorto which is very much the same, and it has a section that says "if it does this then try this and this". that helped me immensely!good luckblair

My most recent weber challenges: 1 - My accel pump diaphragms did not match. One was barely pumping. I found a way to measure how much came out each and found them to be WAY off. Replaced both and it made a world of difference.

2 - If using pump gas (in the US) with ethanol: This WILL clog your jets. As the gas sits in the bowls the ethanol absorbs water, then the gas and ethanol evaporates leaving the water in the bowls to corrode the aluminum. This leads to white powdery deposits in the bowls which will clog the jets. FILTERS do NOT help. (the ethanol destroys the diaphragms in most of our fuel pressure regulators too - they will only last about 1 year in ethanol)

3 - Intake manifold leaks. Sometimes they would leak when hot, but not cold. Do the WD40, starting fluid, or water spray test AFTER the engine has warmed up. see if you can make the engine stumble spraying around the manifold bases, carb bases, and throttle shafts.

If I recall correctly, that engine has a pretty stout cam profile.Between that and the large valves, you will probably never have good off-the-line performance without revving it up and dumping the clutch.That said, try 170 mains and 220 air corr. jets.Going bigger should shrink the flat spot.You may also need to adjust the accelerator pump rods to squirt more fuel.

Also (Kieth) didn't we both notice exceptional improvments in my HPMX40's and your Weber 44's when we tapped and plugged the non-functional choke circuit ports?

Also / agree with the timing function needing to be right on the advance. Mine on the type 4 was 32-34 degrees...... otherwise power was suffering and I would experience lag on start off. (IMG:style_emoticons/default/beerchug.gif)

Thanks for your input.I'm a little short on time to work on the car.Instead of learning about timing, I ordered #34 Venturi's (current size is #36). Just because that was something I could do while doing groceries.

Not sure if this is related, but.The car also comes slow "off its RPM". Meaning when it runs at high RPM and I need to slow down (with foot of the accelerator and clutch pushed in, to downshift), or stop. The engine keeps spinning high for 2 or 3 more seconds.

During up-shifts it sounds like I'm pushing the accelerator between shifts (not the case).